1. Field of the Invention
This invention relates to water-containing cleaning formulations of controllably variable strength based on alkali hydroxide. To establish the solid consistency required, the cleaning formulations according to the invention contain glycols, glycol derivatives and/or certain alkanolamines and alkali hydroxide in solid form.
Highly alkaline cleaning formulations are now commercially available in various forms, for example as powders, granules, liquids, fused blocks or tablets produced by compression molding.
Each form has specific advantages and disadvantages for a particular application. Powders, granules or liquids have been successfully used for cleaning textile surfaces or for the manual mechanical cleaning of hard surfaces while tablets produced by compression molding or block-like cleaning compositions (fused blocks) obtained by melting and subsequent cooling are being increasingly used in addition to powders, granules or liquids for the machine cleaning of hard surfaces, for example for the machine cleaning of crockery. Tablets and fused blocks have the advantage over powders of simple and accurate dosing, do not emit any dust and are easy to handle.
These advantages can be utilized, for example, in domestic dishwashing machines and, above all, in continuous institutional dishwashing machines in which the articles to be cleaned pass through various washing zones.
It has now been found that very hard tablets and very hard fused blocks have disadvantages. For example, tablets can be damaged by breakage; tablets thus damaged obviously no longer afford the advantage of exact dosage. Another problem with tablets is that the required solubility in water cannot always guaranteed, i.e. tablets occasionally dissolve either too quickly or too slowly. Although fused blocks show high resistance to breakage during transportation, these very hard cleaning compositions present dosage problems where they are packed in relatively large containers. In addition, both tablets and fused blocks involve very complicated production processes which impose particularly stringent demands on the materials used and the conditions selected, particularly in the processing of alkaline melts.
The cleaning compositions obtained are also expected to show high homogeneity although this is often difficult to achieve in the case of compact cleaning formulations. This problem does not affect liquid cleaning formulations which can easily be stirred. Accordingly, it would be desirable to have the homogeneity of a liquid, a viscous fluid or a stirrable paste which would then harden into a solid of controllably variable strength in order at this stage to utilize its advantages for storage, transportation and dosage. It would be particularly desirable in this regard if stirrability could be maintained at temperatures of up to about 40.degree. C. because, in that case, even components lacking heat resistance could be incorporated.
The problem addressed by the present invention was to provide highly alkaline general cleaning formulations based on alkalihydroxide, preferably potassium or sodium hydroxide and, more preferably, sodium hydroxide for textile surfaces, but preferably formulations for cleaning hard surfaces, for example crockery, and in particular institutional dishwashing detergents which would combine the advantages of powders and liquids on the one hand with the advantages of tablets and fused blocks on the other hand. In other words, the problem addressed by the present invention was to provide cleaning formulations which would show defined solubility under various conditions of use, but which on the other hand would be stable during transportation and storage and which, in addition, could be dispensed quickly, easily and accurately, would not emit any dust, could be produced without expensive machinery and could readily be packed in containers. The stirrability of the cleaning formulations during their production and their controllably variable strength during production and storage would afford major advantages and should be taken into account. To this end, the invention set out to develop a process which would enable substances lacking heat resistance to be incorporated, if necessary even at temperatures below 42.degree. C., without compromising the other solutions to be provided.
The requirements which cleaning formulations are usually expected to satisfy, such as the development of high cleaning power, fat dissolving power, etc., would of course have to be fulfilled at the same time.
Both relatively high-viscosity to paste-like cleaning formulations and also compact cleaning formulations in tablet or block form are already known from the prior art.
2. Discussion of Related Art
The cleaning compositions disclosed in DE-OS 31 38 425, for example, assume the form of a gel-like paste which is said to exhibit such rheological behavior that it can be liquefied and readily discharged from a spray nozzle by the action of mechanical forces, for example by shaking or by the application of pressure to a deformable storage bottle or tube or by means of a metering pump.
U.S. Pat. No. 3,607,764 describes glass cleaners in compact form which are diluted to form a sprayable solution. These cleaning formulations contain inter alia sodium or potassium hydroxide, sodium or potassium tripolyphosphate, sodium or potassium pyrophosphate, hydroxycarboxylic acid builders, a water-soluble nonionic surfactant, alkylene glycol ether and, optionally, sodium carbonate. The control of viscosity or strength as achieved by the present invention is not mentioned.
JA 84/182870 describes solutions of alkali hydroxides in glycols or alcohols which become viscous through neutralization with long-chain carboxylic acids and which assume a pasty consistency through the addition of silicone oil so that they may be used as pastes in the oiling of leather.
JA 86/296098 describes water-free compact cleaning formulations based on alkali hydroxides. In this case, the alkali carrier is mixed with alkanolamines and water-soluble glycol ethers so that a compact cleaning formulation is obtained. A technical teaching for obtaining a variable reduction in strength is not disclosed.